1. Field of the Invention
The present invention relates to a refrigeration system, and more particularly to a refrigerating system suitable for controlling the capacity of a capacity-variable compressor incorporated in a refrigeration system for use in an automobile air conditioner.
2. Prior Art
In a conventional refrigeration system incorporating a variable-capacity compressor, an axial-piston type of compressor has a mechanism in which a swash plate forming a drive portion for suction and compression can be rotated about a support point, and the angle of rotation of the swash plate around the support point, i.e., the piston stroke of the compressor, is controlled by modifying the pressure within a front cover enclosing the swash plate, i.e., the pressure within a crankcase so that the force acting on the rear surface of the piston is controlled, and by balancing that force and the gas compression force acting on the front surface of the piston. This capacity control method is, for example, disclosed in the specifications of U.S. Pat. Nos. 3,861,829 and 4,428,718. In such a system, the pressure in the crankcase is controlled by controlling the opening of a pressure control valve provided in a passage connecting the crankcase to the compressor suction chamber in such a manner that the pressure of a refrigerant sucked into the compressor remains above a predetermined value, thereby controlling the flow of blow-by gas (this method is disclosed in the specification of U.S. Pat. No. 3,861,829), and, in addition to this, by introducing the discharged refrigerant into the crankcase (this is proposed by U.S. Pat. No. 4,428,718). In the above-described methods, the capacity of the compressor is controlled by controlling the pressure in a large-capacity crankcase, inevitably resulting in a time lag in each control operation. In particular, changes in the capacity of the compressor do not conform to rapid changes in the rotational speed thereof.
Consequently, when a vehicle is running in a city, where acceleration and deceleration of the engine are repeated, the capacity of the compressor may become insufficient, resulting in insufficient cooling.
In addition, in the above methods, heat generated in the crankcase does not escape therefrom because the crankcase is of the enclosed type, deteriorating the viscosity of the lubricant and thereby reducing its lubricating effect.